1. Field of the Invention
The present invention generally relates to an optical-pickup slider using an optical near-field and floating a predetermined distance above a high-density recording medium by an air flow, and a manufacturing method thereof.
The present invention further relates to a probe suitable for gathering incident light and emitting it to a sample to be measured or a recording medium for example, and a manufacturing method thereof, a probe array and a manufacturing method thereof, and, in more detail, to a probe which can gather incident light and generate an optical near-field and/or propagation light, a manufacturing method thereof, a probe array and a manufacturing method thereof.
2. Description of the Related Art
In a high-density information recording device using an optical near-field, as shown in Japanese Laid-Open Patent Application No. 9-198830 for example, recording and reading of information is performed on a recording-medium disc in a condition in which a slider of an optical pickup (optical-pickup slider) floats a distance equal to or smaller than hundreds of nanometers above a surface of the recording-medium disc by an air flow generated due to rotation of the recording-medium disc. As shown in FIG. 1, a slider 61 disclosed in Japanese Laid-Open Patent Application No. 9-198830 has a conical hole 62 passing between a side facing a recording medium and an opposite side formed therein, and has an aperture 63 on the side facing the recording medium. Light is incident from a larger opening of the hole 62 and an optical near-field is generated in the vicinity of the aperture 63.
As shown in FIG. 2, in a head of an information recording device using this slider 61, a light source 11 and a lens 12 are provided on the side opposite to the side of the slider 61 facing the recording medium 14. Light from the light source 11 is incident on the hole 62 of the slider 61 through the lens 12. By this light, an optical near-field generated in the vicinity of the aperture 63 is incident on the recording medium. Light incident on the recording medium has a diameter on the order of a diameter of the aperture 63, and it is possible to increase a resolution in recording/detecting, by this light, to one higher than 200 nm. Recording by this head is such that an energy applied to the recording medium 14 is changed, as a result of an intensity of light from the light source 11 being changed, and information is recorded on the recording medium 14. Further, detecting of information is performed using a photodetector 64 arranged on a side of the recording medium 14 opposite to a side facing the slider 61. Specifically, an optical near-field generated at the aperture 63 of the slider 61 generates propagation light as a result of contacting the recording medium 14, and the propagation light is detected by the photodetector 64, and, thus, information written on the recording medium can be detected. Thus, high-density recording can be performed using an optical near-field.
Further, M. B. Lee, T. Nakano, T. Yatsui, M. Kourogi, K. Tsutsui, N. Atoda, and M. Ohtsu, “Fabrication of Si planar aperture array for high speed near-field optical storage and readout”, Technical digest of the Pacific Rim Conference on Laser and Electro-Optics, Makuhari, Japan, No. WL2, pp. 91–92, July 1997 discloses, as shown in FIG. 3, a near-field optical probe 71 in which an inverse conical hole is formed in a silicon single-crystal substrate. When this probe 71 is made, a silicon single-crystal substrate 72 having thermal oxidation films 73 formed on both sides thereof, having a thickness of 270 μm and having (100) plane orientation, as shown in FIG. 4A, photo resist 74 is coated on the thermal oxidation films 73, and an opening of 10 μm×10 μm is formed by photolithographic etching, as shown in FIG. 4B. Then, as shown in FIG. 4C, single-crystal anisotropic etching of silicon is performed by KOH solution of 80° C. and a concentration of 10 weight %. Thereby, an inverse-pyramid-shaped hole 75 surrounded by a (111) plane of the silicon single-crystal substrate is formed. Then, as shown in FIG. 4D, photo resist 74 is coated on both sides, and a thermal-oxidation-film pattern having a large opening is made on the reverse side by photolithographic etching. Then, as shown in FIG. 4E, single-crystal anisotropic etching of silicon is performed from the reverse side by KOH solution again. At this time, the etching is stopped so that a through hole on the order of sub-microns is formed on the bottom of the pyramid-shaped hole 75. The etching is stopped so that the opening dimension equal to or smaller than sub-microns can be obtained as a result of an etching speed being previously measured and a time of etching stoppage being controlled. Then, as shown in FIG. 4F, fringes of the thermal oxidation films are removed by a dicing saw or by etching. Then, as shown in FIG. 4G, gold 76 is spattered, and, thereby, laser light is prevented from being incident on a recording material through portions other than the openings. Further, for assuring that the etching is stopped just in time, as shown in FIGS. 5A through 5G, an SOI (Silicon-On-Insulator) substrate 78 having an SiO2 film 77 in the middle is used. By this method, it is possible to obtain an opening having a diameter of 200 nm in a substrate.
An opening having a diameter equal to or smaller than 200 nm is formed on a side facing a recording medium in a slider disclosed in Japanese Laid-Open Patent Application No. 9-198830, and an evanescent wave is generated from this hole. However, this document does not disclose how to obtain this aperture, concretely. The slider has a thickness of millimeters in general, and it is not easy to form a very small aperture equal to or smaller than 200 nm through this thickness. Somewhat special technical measure is needed.
Further, the near-field optical probe shown in FIG. 3 is made, as a result of, as shown in FIGS. 4A through 4G, the inverse-pyramid-shaped hole being formed by anisotropic etching, and, then, the large opening being formed by etching from the reverse side. In this case, the opening dimension of the minute hole is determined by the depth of etching from the reverse side. In order to stop the etching just in time so as to obtain the opening dimension of tens of nanometers, the etching time of the reverse side is previously measured, and, thereby, the etching time is determined. However, thickness of silicon substrates varies on the order of tens of microns among the substrates. Further, an etching speed varies in a wide range depending on an amount of silicon dissolved in an etching liquid, an amount of oxide dissolved in the etching liquid, a slight temperature difference, and so forth. Accordingly, it is actually very difficult to stop etching just in time so as to achieve an opening dimension of tens of nanometers from a previously measured etching speed and a substrate thickness.
It is possible to obtain a desired small opening on the order of 50 nm with high repeatability by using an SOI substrate, and using an SiO film embedded in the middle as a film for stopping etching from a reverse side, as shown in FIGS. 5A through 5G. However, a thick fringe is produced around a surface on which the small opening is produced. Thereby, in this condition, it is not possible that the opening approaches a recording medium to a distance of tens of nanometers. Therefore, it is necessary to remove this fringe. However, because a thickness of a portion having the opening is on the order of 10 μm it is likely to be destroyed when or after the fringe is removed. In order to avoid such a situation, as shown in FIG. 6C or FIG. 7C, a thickness of a portion of a silicon substrate 72 in which an opening is provided is made small. Then, as shown in FIG. 6E or FIG. 7E, a pattern of silicon oxide for performing etching for providing the opening is formed on a bottom obtained by etching. Then, as shown in FIG. 6F or FIG. 7F, a hole 75 is formed by anisotropic etching. However, in this case, as shown in FIG. 6E or FIG. 7E, when photo resist 74 is coated, because a level difference of hundreds of microns exists from a surrounding fringe portion, it is not possible to coat the photo resist uniformly, and to form the pattern of silicon oxide with high accuracy.
A plurality-of-projection probe provided in a near-field optical microscope or a near-field optical recording optical head are made by a method in which an array of a plurality of recesses is transferred, in the related art, for example.
This near-field optical microscope or near-field optical recording optical head has a projection-type probe array arranged so that a distance between each projection and a sample is smaller than a wavelength of light used when the sample is measured. Thereby, the near-field optical microscope can measure physical properties of the sample by generating an optical near-field between each projection and the sample.
When the above-mentioned projection-type probe array is manufactured, first, a recess array having a plurality of recesses is made in an Si substrate as a result of anisotropic etching being performed on the Si substrate having a plane orientation of (100) plane for example. Then, the recesses are transferred onto another material such as metal material or dielectric material for example using the thus-made recess array. At this time, a surface of the recess array is covered by the material, such as metal or dielectric, other than Si. Then, the Si substrate is removed from the other material. Thereby, a projection-type probe array provided with a plurality of projections made of metal material or dielectric material is made.
The above-described projection-type probe array provided in the near-field optical microscope is used in a condition in which a distance between each projection and a sample is equal to or smaller than a wavelength of light. Therefore, it is important to control a height of each projection properly.
When a projection-type probe array is made as a result of a recess array being transferred onto a metal material or the like, a height of each projection is, as shown in FIG. 8, determined by a depth of a recess 1001 of the recess array 1000. The depth of each recess 1001 is determined by a width of the recess 1001 W=2H/tan 54.74°≈1.414H because the recess 1001 is surrounded by an Si (111) plane. (The symbol ‘≈’ signifies ‘is approximately equal to’.)
However, the width of each recess 1001 involves an error on the order of approximately 10 nm due to variation in mechanical accuracy even when an electronic-beam exposing device is used. Accordingly, it is not possible to make uniform heights of respective projections of a projection-type probe array made by using the recess array 1000.
Further, when a single-projection probe is made, the above-mentioned problem involved in manufacturing of a projection-type probe array does not arise. However, the following problems arise.
First, a tip of a projection is not pointed, but, actually, is worked to a plane, and, thus, the projection is shaped as a truncated cone or pyramid. When a truncated-cone-or-pyramid projection is made in the related art, as shown in FIG. 9A, first, a truncated-cone-or-pyramid recess 3001 is made. Then, as a result of this being transferred, a projection is made. At this time, a planarity of a tip of the projection reflects a planarity of a bottom of the above-mentioned recess. When the recess having a bottom surface 3002 is made, a time of anisotropic etching is controlled and the etching is stopped before the entirety of the plane constituting the recess 3001 becomes a (111) plane (no bottom surface remains). In this case, a planarity of the bottom surface 3002 may deteriorate much due to a hillock or the like produced.
A planarity equal to or less than λ/8 is needed for a tip of a projection-type probe, assuming that a wavelength of light to be emitted is λ, for example. However, a planarity of the bottom surface 3002 of the recess 3001 made in the related art is far from reaching this. Accordingly, it is not possible to make a satisfactory projection-type probe by the related art.
Further, as shown in FIG. 9B, there is a case where an etch stop layer 3003 is previously made, and a bottom surface 3002 is obtained, when a recess 3001 is made, without controlling a time of etching. In this case, because it is possible to obtain a satisfactory planarity of the etch stop layer 3003, it is possible to make a projection-type probe satisfactory in a planarity view point.
However, in this case, a diameter of an opening D of a projection to be made is determined by an opening width W of the recess 3001 and a depth H of the recess 3001. The depth H has a sufficient accuracy in a local planarity view point as described above. However, variation within a sheet of wafer or between wafers may be very large as much as on the order of hundreds of nanometers.
Accordingly, when recesses 3001 are made to have uniform opening widths W, diameters of bottom surfaces 3002 (that is, diameters of openings at tips of projections) vary depending on variation in depths H.
In order to cope therewith, an opening width W may be made to change correspondingly to a variation of a depth H. However, it is not possible to measure a depth H precisely. Furthermore, it is not possible to change a dimension of a photo mask, actually.
Thus, even manufacturing of a single-projection probe which does not need consideration of making uniform heights of a plurality of projections involves problems on dimension accuracy in the related art.